Combine Ground Beef, bread crumbs, egg white and seasoned salt in medium bowl, mixing lightly but thoroughly. Lightly shape into four 1/2-inch thick patties. Brush onion slices with 1/2 tablespoon oil.
Place patties and onion slices on grid over medium, ash-covered coals. Grill patties, covered, 8 to 10 minutes (over medium heat on preheated gas grill 7 to 9 minutes), until instant-read thermometer inserted horizontally into center registers 160 degrees F, turning occasionally. Grill onions, 11 to 13 minutes or until tender, brushing with remaining 1/2 tablespoon oil and turning occasionally.
Line bottom of each bun with lettuce. Place tomatoes and burgers on lettuce. Spoon dressing over burgers; top with onions. Close sandwiches.